You've attached a bungee cord to a wagon and are using it to pull your little sister while you take her for a jaunt. The bungee's unstretched length is 1.3m and you happen to know that your little sister weighs 220N and the wagon weighs 75N. Crossing a street, you accelerate from rest to your normal walking speed of 1.5m/s in 2.0s, and you notice that while you are accelerating, the bungees length increases to about 2.0 cm. what is the force constant of the bungee cord, assuming it obeys hooke's law?
The Attempt at a Solution
Ok, so I am quite stumped with this question, i know you should find the total force of the little sister and wagon , 220+75, but i do not know if i should keep it as a force or as a total mass in kg. And the difference in spring length 2.0-1.3=.7m . I am just unaware if i bring kinematic forumlas into this and i am quite unaware of what to find because i am getting the wrong answer when looking for "k"
Any guidance is appreciated. Thanks